Free turbine turbo-propeller engines have relatively poor in-flight windmill characteristics. High airspeeds must be achieved to get core wind-milling speeds and internal flow up to a point where the engine may be re-started without external power assist. In some cases, it may be necessary to fly at 70 to 80% cruise airspeed for satisfactory pure windmill starts. To achieve this with one or more unplanned shutdown of an engine, it would be necessary to put the aircraft into a dive with a resulting loss of altitude. This option may not be available close to the ground. To restart at lower speeds, it is necessary to use aircraft power or battery power to assist the start. Using the engine starter motor battery power alone may not be sufficient to start a large high pressure ratio free turbine turboprop. This means that certain unplanned engine shutdown cases addressed by current turboprop aircrafts, which can battery start in-flight, are not covered without an additional energy power source on the aircraft.